This invention relates to processes for the production of fluorinated organic compounds. More particularly, the present invention relates methods for producing fluorine-containing compositions containing advantageously low levels of water.
There are numerous processes directed to the manufacture of fluorinated organic compounds and to compositions containing such compounds. Many of these processes involve the reaction of an organic compound, such as a chloroalkane or chloroalkene, with hydrogen fluoride (HF) in the presence of a fluorination catalyst. In several of these processes, water is present in one or more of the reaction product streams containing the desired fluorinated organic compound. This water may originate as an impurity in the reactants or other starting materials. The water also may be formed as a byproduct from the reaction process, including reaction of HF with the catalyst, and/or as a product of the catalyst regeneration process.
It has been recognized that mixtures of water and hydrogen fluoride are especially corrosive, and that this combination is both difficult and expensive to handle. As a result, it is typically desirable to remove water from those portions of the fluorination processes where it is exposed to HF, including in product streams, byproduct streams, reactant streams, and recycle streams. Moreover, water which is present in the fluorination process, even at low levels, may act as a catalyst poison, thereby having deleterious effects on the effectiveness, efficiency, selectivity and/or yield of the fluorination reaction.
Several methods of removing or reducing the amount of water from fluorination process streams have previously been proposed. For example, U.S. Pat. No. 5,334,784 (Blake, et al.) and U.S. Pat. No. 6,103,944 (Blake, et al.), suggest distillation as a method for physically removing water from a fluorination process stream. U.S. Pat. No. 6,111,151 (Ewing, et al.) discloses phase separation as an alternative method of physically removing undesirable water from the process stream. In addition, drying agents such as sodium polyacrylate (U.S. Pat. No. 6,101,818, Thomas, et al.) and calcium chloride (U.S. Pat. No. 5,723,702, Kwon, et al.) have also been suggested as a means to absorb water from a process stream. While Blake, Ewing, and others in the field have attempted to remove water from the reaction product by using equipment and methods downstream of the fluorination reactor, such as those described above, these processes are inherently expensive. Moreover, known absorbents that are compatible with the fluorination reaction are not selective for water and therefore cannot generally be used to advantage during the fluorination process. Each of the aforementioned methods also pose a further disadvantage in that they can only remove water downstream of the process reaction, and therefore they are not effective for the removal of water at the reaction site and cannot prevent catalyst poisoning.
Process streams downstream of the fluorination reaction typically contain unreacted organic materials and unreacted HF in addition to the desired fluorinated compounds. To increase product yield, it is common to separate the un-reacted starting components from the product stream and to recycle HF and/or the under fluorinated components back to the reaction step. Because recycling tends to increase the concentration of water present during the fluorination reaction, it is advantageous to remove any water from the product stream prior to recycling.
The present inventors have come to appreciate a need in the art for an improved fluorination process and for improved fluorine-containing compositions, preferably fluorine substituted organic molecules having from about 2 to about 5 carbon atoms. We have discovered that this need can be satisfied by introducing to one or more fluorination process compositions a water reactive agent in an amount and under conditions effective to decrease the amount of water in that composition. By applying this teaching, the fluorination process and the products produced thereby can be improved. Furthermore, the present inventors have recognized that water can have a deleterious effect not only on the processing of the reaction product downstream of the reactor, but also on the fluorination reaction itself. In view of this recognition, applicants have discovered a fluorination process which preferably comprises introducing to the fluorination reaction process, preferably at a location proximate to the site of the fluorination reaction and/or upstream of the fluorination reaction, a water reactive agent in an amount and under conditions effective to produce a relatively lower concentration of water in the reaction mixture, and preferably throughout the fluorination process.
As used herein, the term xe2x80x9cwater reactive agentxe2x80x9d refers to one or more elements and/or compounds which react either directly or indirectly through the production of intermediate compound(s), with water present at one or more locations in the fluorination process to effectively reduce the molecules of water present in the process stream or composition. As used herein, the term xe2x80x9cfluorination processxe2x80x9d is intended to refer to and include the fluorination reaction itself as well as upstream processing (such as preheating, catalyst treatment, and the like), and downstream processing (such as component separation and the like). Thus, the term xe2x80x9cfluorination processxe2x80x9d includes the location or site of the fluorination reaction and also the streams which are fed to or withdrawn from the reaction site or vessel. In preferred embodiments, the water reactive agent is reactive under conditions which exist at one or more locations in the fluorination process. In other words, the water reactive agent is preferably added to the fluorination process at one or more locations in the process without requiring any substantial alteration of the fluorination reaction conditions, and even more preferably also without requiring any substantial alteration of the upstream and downstream process conditions.
It is also generally preferred that present methods effectively reduce the amount of water at one or more locations in the fluorination process without introducing, directly or as a reaction product, any substantial amount of deleterious new compounds to the process. As used herein, a xe2x80x9cdeleterious compoundxe2x80x9d is one which is either not readily removed from the process or which must be introduced at a location in the fluorination process that has a negative effect on the operation of the fluorination reaction. For example, a water reactive agent which is a poison to the catalyst used in the process, or which causes the formation of a catalyst poison, would be considered a deleterious compound if such a water reactive agent must be inserted into the process at a location or under conditions which cause this negative effect on the fluorination reaction. A compound that is otherwise already present in the process would generally not be considered a deleterious compound. It is preferred in certain embodiments that the presence of the water reactive agent of the present invention does not cause the presence of any substantial amount a new reaction product to the fluorination process. As used herein, the term xe2x80x9cnew reaction productxe2x80x9d refers to a compound or element that is otherwise not normally present in the fluorination reaction product stream or which would require a substantial alteration of the process to accommodate. Thus, it is optional in certain embodiments for the water reactive agent itself to comprise a compound, or combination of compound(s) and/or element(s) that are otherwise already present in the reaction product stream.
In preferred embodiments of the present invention, the water reactive agent comprises a compound having the formula I as follows:
XRyxe2x80x83xe2x80x83(I)
where
X is Cxe2x95x90O or Sxe2x95x90O,
each R is independently H, alkyl, or halogen, provided that at least one R is halogen, and y is 2.
In preferred embodiments, the water reactive agent comprises at least one compound containing a carbonyl or a thionyl group, more preferably a halogen substituted, aliphatic compound containing a carbonyl or a thionyl group, and even more preferably a chlorine substituted, aliphatic C1-C5 compound containing a carbonyl or a thionyl group. For the purpose of convenience, the terms C1, C2, etc. are used herein to mean compounds having one carbon atom, two carbon atoms, etc.